Figure 3.9: The transmission of the boron filter of the ROSAT PSPC
as a function of energy. Note that this filter only
covers the centre of the PSPC field of view.

The spectral resolution of the PSPC in the carbon window
below 0.28keV is 80% (FWHM).
A further subdivision of the carbon band into two bands is possible since
the boron filter has little transmission between 0.188keV and 0.28keV.
The boron filter itself consists of a carbon film with a coating
of boron carbide. The whole structure is supported by a tungsten wire
mesh with a thickness of and spacing of 4mm.
The filter itself has a diameter of 28mm (40'),
hence only the central portion of the PSPC FOV is covered.
The rest of the PSPC FOV is open.
The transmission of the boron filter as a function of energy is shown in
Fig. 3.9.